I've been on both sides of the collective bidding coin, consigning and as a bidding partner. I agree with Barry and others that it actually many times helps the seller because collectors will get together to bid on and buy a lot/set when each collector only needs a portion of the total lot/set.
I don't consider it in any way collusion because I know on the last three or four sets I have bid on with others, I and several others of the partners wouldn't have been able to financially bid on and buy the whole item and thus would have been knocked out of the bidding. Thus the "cabal" style bidding did not reduce the number of bidders and thus lower the final price for the seller but instead kept a very active and competitive bidder involved and brought the price up.
Just my 2 cents.....
